This invention relates generally to novel glass reinforced thermoplastic polyolefin compositions, including a high molecular weight aromatic polycarbonate resin to improve ductility in the final article. The compositions are particularly adapted for injection, extrusion and transfer molding. Further, the compositions produce, when molded or extruded, articles which have excellent physical properties.
It is known from the prior art, e.g., Hattori et al, U.S. Pat. No. 3,639,331, that it is difficult to provide uniform dispersions of fiber glass filaments, glass threads, or roving, in compounded form with suitable molding plastics such as polystyrene, acrylic resins, polyvinyl chloride resins, polysulfone resins, polyester resins, polyolefin resins, polycarbonate resins and the like.
In the said '331 patent, it is proposed to overcome these problems by adding a small amount of dispersion aid which can be, for example, a high viscosity hydrocarbon lubricant, a plasticizer or a low molecular weight resin. It is also known that polyolefins, such as polyethylene and polypropylene can be filled with glass to provide reinforced composites, but these generally have rather poor impact properties and an undesirable brittle mode of failure. In Example 4 of the '331 patent, the dispersion of a crystalline polypropylene-20 percent glass composite is reportedly improved by adding a small amount of a low molecular weight polypropylene--but there is no disclosure of any effect on the impact strength of the resulting composite.
It has now been discovered that composites of polyolefins and glass can be significantly improved in terms of a more desirable ductile mode of failure and better weld line and knit line strength if a high molecular weight aromatic polycarbonate resin is added in minor proportions as a modifier. The results obtained are surprising in light of the prior art, especially the '331 patent, which states that the low molecular weight resin can comprise generally any thermoplastic resin, such as polyethylene, polypropylene, nylon and others, so long as the melt flow (ASTM-D-1238) is from about 50 to 250 grams per 10 minutes or even higher, e.g., up to 5,000 grams per 10 minutes. The high molecular weight aromatic polycarbonates used herein have a much lower melt flow, e.g., in the range of 2.8 to about 20 grams per 10 minutes.